How a small “subterranean hydrocarbon seep” put a lot of nasty benzene into hundreds of thousands of gallons of water

Benzene is a highly flammable volatile organic compound used in the manufacture of plastics, rubber, resins, synthetic fabrics, paints and dry cleaning chemicals. It can also be found in car exhaust or cigarette smoke, or it can form naturally, in volcanoes, forest fires and crude oil.

Benzene is added to gasoline to increase octane. Automobile emissions are the main source of benzene in the environment, but it is more likely to arrive in water by way of industrial discharge or landfill leaching.

Health Effects of Benzene

Benzene is toxic in small doses. According to the EPA, acute benzene exposure above the maximum contaminant level (0.005 milligrams per Liter) can cause “temporary nervous system disorders, immune system depression [and] anemia.” It’s also a carcinogen, and can lead to “chromosome aberrations” with long-term exposure.

An event that scarcely made national news, a small leak at a gas processing plant in western Colorado, put out enough benzene and other nasty chemicals to pollute hundreds of thousands of gallons of groundwater. The description of the cleanup, which we’ve excerpted below from an AP story by Alexandra Tilsley, gives a step-by-step description of the elaborate process necessary to contain even a small “seep” at a petroleum processing plant.

The obvious questions that arise from such incidents are how effective is the cleanup, that is, how much of the contaminant is actually removed in the process, and how many such seemingly insignificant “seeps” go undetected and therefore never treated.

Tilsley writes:

DENVER — As vacuum trucks continue to suck up tainted groundwater from the site of a hydrocarbon leak near a stream in western Colorado, those in charge are beginning to think about the next step: what to do with all that dirty water.

About 180,000 gallons of contaminated water have been pumped out of the ground since the subterranean hydrocarbon seep was discovered near the Williams gas company’s Parachute processing plant, which sits close to Parachute Creek.

One of the main contaminants in the groundwater is benzene, according to Mark Salley, a spokesman for the Colorado Department of Public Health and Environment, which is currently overseeing the remediation efforts. Benzene, a known carcinogen, was also found earlier this month in Parachute Creek in concentrations above the state’s health standard, but levels have since dropped and officials insist there is no threat.

To remove the benzene from the creek, Williams injected air into the surface water to strip the hydrocarbons, a process known as air-sparging. The same technique is [used] to remove surface hydrocarbons that are floating on top of the groundwater.

How to handle all the benzene-infected groundwater is the next question. The recovered water is currently being stored in tanks, and Williams said Friday it is planning to install a water treatment system that can separate the benzene from the water.

“They’re working on the plans right now for a water treatment system,” said Tom Droege, a Williams spokesman. “It’s not in place yet, but once it’s up and running, then they’ll begin to treat the groundwater on a regular basis.”

The system will remove the benzene and any other hydrocarbons from the water through a multistep process. Contaminated water will first go through an oil and water separator. Then, it will move through an air stripper, which works like air-sparging. Finally, the water will be moved through activated carbon polishing tanks.

The treated water will then return to a holding tank, where it will be tested to ensure it meets state health department and U.S. Environmental Protection Agency standards. Once officials have confirmed the water is safe, it will be returned to the aquifer.

Any air emissions from the treatment system will be captured and treated according to the procedures approved by the Air Pollution Control Division of the state’s health department, Salley said.

The system is expected to be functional by the end of May.

An effective home water treatment (point of use or point of entry) for benzene is activated carbon. As with other volatile organics, benzene is best treated with coconut shell carbon because of its very tight pore structure, but any good carbon can be effective.